1. Field of the Invention
This invention concerns a copolyamide acid and a copolyimide of a novel structure having extremely high heat resistance, elasticity and strength.
2. Description of the Prior Art
There is known a copolyimide which is produced by copolymerizing pyromellitic anhydride and 4,4'-diaminodiphenyl ether (Japanese Patent Publication No. 10945/1962).
However, this copolyimide does not have sufficient elastic modulus and strength, and there is a continuing need for a copolyimide having high elastic modulus and strength.